This application relates to radio frequency devices, and more particularly, to opto-electronic devices and techniques for processing and transmitting radio frequency signals.
Optical waves can be used as carriers to transmit radio frequency (RF) signals from one location to another. In addition, the characteristics of a RF signal may be modified by optical techniques. This combination of RF technology and photonic technology can be used to achieve certain advantages and provide new devices and applications in signal processing and communications.
Brillouin selective sideband amplification of a RF signal is one example of combining RF technology and photonic technology for new devices and applications. See, U.S. Pat. No. 5,917,179 to Yao and U.S. patent application Ser. No. 09/006,845 filed on Jan. 14, 1998 by Yao (allowed and to be issued). An optical pump beam can be injected into a Brillouin optical medium to produce an acoustic grating moving in the direction of the pump beam based on the electrorestrictive effect. This grating interacts with the pump beam to produce a backscattered Brillouin optical wave at a frequency less than that of the pump beam.
When a narrow-band seed signal in the opposite direction of the pump wave and at the same frequency of the Brillouin optical wave is injected into the medium, the interaction between the seed signal and the pump wave can significantly enhance the acoustic grating and convert the spontaneous Brillouin scattering into a stimulated Brillouin scattering (SBS). The stimulated back scattering light adds up in phase with the seed signal to produce an amplified seed signal. This Brillouin amplification can be used to implement a signal amplification scheme to selectively amplify a RF sideband in a modulated optical signal. The narrow bandwidth of the Brillouin amplification is used to selectively amplify one or more desired RF sidebands and to leave the strong carrier signal essentially unchanged.
The present disclosure includes systems and techniques for transmitting and processing a RF signal by using opto-electronic devices based on the Brillouin selective sideband amplification.
In one embodiment, a photonic RF link may be configured to achieve a number of signal processing operations in the optical domain, including frequency up or down conversion and signal amplification. The processing operations in the optical domain may be insensitive to the polarization state of light and substantially free of the fiber dispersion effect after transmission through a fiber link. Such a photonic RF link may also use low loss and less expensive optical phase modulators to avoid modulator bias problems in some optical intensity modulators.
For example, such a device may include an input terminal to receive an input electrical signal and an opto-electronic module. The module includes an optical amplifier with a Brillouin medium which produces a pump beam in the Brillouin medium to generate a Brillouin signal, and an optical ring unit which has an optical modulator to superimpose the input electrical signal onto an optical signal. The optical ring unit is adapted to couple the optical signal into the Brillouin medium in a way that its polarization is substantially identical to a polarization of the pump beam to selectively amplify a sideband in the optical signal. A photodetector is also included to convert the amplified optical signal into an output electrical signal.